Mal-aligned teeth detract from the aesthetic appeal of a smile and impart a negative image of the wearer of the smile. Therefore, straightening and aligning mal-aligned teeth has gained in popularity over the years. Correcting mal-aligned teeth is the exclusive domain of orthodontists who use various implements and procedures to align a patient's teeth. The underlying principle in aligning mal-aligned teeth involves forcing movement of the mal-aligned teeth from their designated positions and re-positioning them to align with the rest of the teeth. To accomplish this method of orthodontic tooth movement, orthodontists use different appliances. The most commonly used orthodontic appliance is the edgewise appliance and its variation, namely the straight wire appliance.
The edgewise appliance system uses a combination of many individual pieces designed to function in a coordinated fashion. The two primary components of this system are, 1) tooth attachments in the form of brackets and bands, and 2) arch wires that engage the brackets and bands. These attachments which are semi-permanently and rigidly attached to the teeth serve as a handle by which force generated by the wires may be transmitted to the teeth to accomplish orthodontic tooth movement. Each attachment in this system is comprised of an orthodontic bracket bonded to the teeth with adhesives and having a rectangular slot that is capable of receiving and accommodating an arch wire with a round, rectangular or square cross section. The arch wires are held within the bracket slot using ligature ties and are a removable component of the system. During treatment, the orthodontist removes the arch wire and makes adjustments to the same wire or inserts new wires in the bracket slot. The optimum three dimensional movement of the tooth is accomplished when the rectangular slot of the bracket is completely or nearly completely filled by a rectangular arch wire. Even with the rectangular arch wire completely filling the rectangular slot of the bracket, all three degrees of control or movement of the teeth may not be efficient due to the bracket-wire play which is essentially brought about by the difference in size of the bracket slot and the arch wire engaged in that slot. Typically, elastic deflection of the arch wire generates forces that are transmitted to the teeth by the brackets attached to the teeth, thereby causing the teeth to move to a desired position. The degree of elastic deflection of the arch wire in turn depends on the properties of the material used in the construction of the wire and the size, shape and cross section of the arch wire.
In a straight wire appliance system, the angulations and inclinations of the teeth are built into the bracket eliminating the need for bending the arch wires to accomplish tooth movement. In theory, the brackets are rigidly fixed to the teeth at their precise pre-programmed or pre-adjusted positions on the mid-facial or lingual aspect of the teeth at their respective mal-aligned positions. The straight, flat, wire is then deflected to engage the bracket slots. The force generated by the elastic deformation of the wire then pulls the teeth along with it as it moves to its original shape, thereby aligning the teeth. Due to the inherent structural differences in tooth size and shape, while the general shape of the bracket may be very similar, for each particular tooth type the corresponding bracket is designed with specific compensation in the base shape, base size, general shape, slot angulations, base thickness etc, to accommodate for differences in tooth shape, size and its spatial relation relative to the horizontal plane.
Initial stages of the orthodontic treatment are accomplished using small size round wires. Although a relatively thinner wire having a round cross-section does not allow application of torquing (labio-lingual inclination of tooth) forces when engaged within an arch wire slot, it does provide a greater degree of flexibility and generally applies less force in use, which is more comfortable for the patient. The characteristic low force of round arch wires is due to their thinner cross-section. As such, wires having a round cross-section are often useful during the beginning stages of orthodontic treatment when the teeth are most mal-aligned. Use of a round arch wire allows for movement of teeth to correct mainly angulations and rotation with relatively light and therefore more comfortable forces. In this phase, the wire is loosely held in the bracket slot to allow sliding of the wire with minimal friction so that the brackets and the teeth attached to them are moved into alignment. A form of brackets called self-legating brackets have been claimed to perform better in this phase due to passive ligation and minimal forces exerted on the wire, consequently resulting in low friction. Once these corrections have been achieved, a relatively thicker square or rectangular wire typically replaces the round arch wire so as to allow torquing of selected teeth to accomplish labio-lingual inclination of the teeth. Torquing is the most difficult tooth movement to accomplish due to small moment arm. Torquing requires use of thicker and stiffer rectangular wires that engage the bracket slot completely (to avoid play). The use of such wires generates heavy forces that have been documented to cause undesirable side effects like orthodontic root resorption.
The conventional orthodontic treatment systems thus described are a cumbersome process and the bracket-wire interaction during the treatment lacks complete three dimensional control, especially in the initial stages of orthodontic treatment. The orthodontic bracket of the present invention can facilitate a true three dimensional movement of the teeth, bringing them into alignment during the entire orthodontic treatment period because all movements can occur simultaneously to move the teeth from their initial mal-aligned stage to the final aligned stage thereby shortening the treatment time, as opposed to conventional orthodontic treatments where a three dimensional control is achieved only in the later stages of the treatment. In general, the orthodontic bracket of the present invention addresses many limitations of conventional orthodontic treatments.